Electrical apparatus



Feb. 5, 1946. A, poTTlNGER l A v2,394,102

ELECTRICAL APPARATUS Filed Sept. 19, 1944 ,v2/ae ,4er v 3 OOOOO BY OO O ai' O O f l EYfMj ATTORN Patented Feb. 5, 1946 AlexanderPottinger, Hamilton, Ontario, Canada, assignor to Westinghouse 'Electric Corporation, `East Pittsburgh, Pa., a corporation of Pennsyl- Vania.

Application September 19, 1944, VSerial No. 554,843

(Cl. TML-119) '8 Claims.

'My invention relates to apparatus for adjustthevvoltage of .alternating-current electric .circuits such vas regulating transformers vof the tap- .changing type in which tap-changing'equipment is operated while the transformer fis under load. More particularly, my inyentionisrelated to :improvements in the tap-.changing :circuit connections .for such transformers.

In maintaining the voltage `supplied to load centers .constant ,through .distribution or feeder circuits, regulating apparatusis required to .compensate for Avariations inthe voltageof the 'power source and for ychanges in `the circuit impedance drop which result fromload demandfluctuations. `My invention is directed'to step-.type voltage `regulaters or tap-changing transformers which, because of their low cost and .other desirable .characteristcs, are particularly well .suited for application to feeder circuits of .the relatively :highvoltage low-current ratings which are prevalent -in 7certain .distribution systems.

In regulating transformers of l.the .tap-changing type, a preventive reactor is commonly .used to effect .the transition from one tap'position'to lanother tap position `of the equipment. In certain situations, it is .desirable to .employ t-wo pairs yof switches in parallel, connecting the tap .polnton the transformer winding to ya feedercircuit conductor, in `order `:to increase .the currentcarrying capacity of the equipment.

resistances are the same, one will carry more than its share of the total `current so that .the .combined current carrying :capacity vof the .two

switcheswill be appreciably less than double that ofone switch. .In accordance with the invention, means is provided for forcing substantially .equal .division .of current between the two 1switches so as .to allow the rating .of each -4pair of switches to .be twice that A.of ka single switch.

Itis an object of the invention .to providein a tap-changingsystem of the labove-findicated character, two tapswitches .associated withveach .transformer 4vtap `point tor `rconnecting .the tap V.connection from that tap-point lto 1.a maincircuit conduc- 4.tor vand to provide means for effecting .arsubstantially equal :division of current flow between them.

.Other objects and advantages of the invention will be apparent from the following description of a .preferred .embodiment thereof, reference being hadfto theaccornpan-ying drawing, in which:

Figure 1 -is a diagrammatic view of apparatus and circuits comprising a Prion-art -tapfohanang system;

Normally, when rswitches are .connected in parallel, :unless their circuits illustrating a Yniod'ication of the system ,shown in Fig. 1;

Fig. 3'is .a diagrammatlcview of apparatus and circuits arranged in accordance with my inven- --tion and Fig. 4 is a .chartshowing the :sequence ofopera- `tion .of Vthe several `switches utilized by the tapchanging system illustrated in Figs. 1 2 and .3.

Referring to the drawing, and particular-ly'to Fig. 1, van autotransformer winding I is illustrated and is connected .to be supplied with energy from .a suitable source throughcircuit conductors 2 and 3 that are connected to the winding terminals 4 .and 15 and to .deliver energy to .a secondaryor `feeder circuit represented by conductors l and 3.

.A'preventive reactor 'I is shown having a midpoint 9 connected .to the .secondary circuit con- -ductor `6, and'terminals II and I2 that are adapted to be connected to selected tap points on the transformer winding I represented by the winding terminal! and the intermediate tap points I 3, III, I5 and I6. ATap conductors 2|, 22, 23, 24and 25 extend from the above-indicated tap points and` connect to one terminal respectively of tap ,switches A, B, C, D and E. The remaining termnalsvof the tap switches are `connected to vone ofthe terminals I I or I2 of the ,preventive reactor I. The .lower terminals of `tap switches A, C `and E,for example, are shown .as connected ythrough circuit conductors'26, 21 tand`128, respectively, .to the Vreactor end terminal II and the vlower terminals of switches B and ,-D .are `shown as connected through circuit conductors SI and .32 tothe .opposite end terminal I2 of .thereactor 'I. A short circuiting switch LF is shown for yconnecting the terminals I I and I2 .of the .preventive reactor 'I together under certain steps in the sequence of operation of the apparatus, `asindicated in the chart Ashown vin Fig. 4.

In the .chart of Fig. 4, the switches A, B, C, D, E vand F are indicated inthe vertical .column .atythe left .of the chart andthe tap positions .II 4to 9 are indicated along the Ytop of the chart'there being a space'between `each .one of the Vnumbered columns y representing an intermediate stepin the tap-changing operationfrom one tap position to the next tap vposition in the sequence of yoperation of the equipment.- The presence of a circle `opposite any one of the indicated switches in.-

.dicates that the switch is closed in that position `of the voltage .adjusting equipment, .and

the `absence of a circle indicatesthat the switch is in its circuit-.interrupting position. Thus; .in

thefirst position yof the voltage-.adjusting mecha- Fig. Zisa diagrammatic view ofappamtusand 55 yrnism, under the column indicated 'by the numeral I, the tap-changing switch A and the short-circuiting switch F are closed and all other tap-changing switches are open. The secondary circuit conductor E is, therefore, connected to the primary circuit conductor 2 through the two halves of the preventive reactor 1 in parallel from the terminals II and I2 to the midpoint; 9. The preventive reactor is so arranged that when current flows in this manner through it, the reactance is substantially nil, while when current flows in either direction through the entire winding between the terminals II and I2 an appreciable reactance exists. As the tap-changing system operates, the several switches are operated in a sequence shown in the chart in Fig. 4 by mechanism not shown in the drawing. When the voltage adjusting mechanism is operated from position I to position 2, the short-circuiting switch F is nrst opened, thus connecting the conductor 2 to the conductor 6 through one-half only of the reactor winding 1, placing temporarily a certain reactance drop in the circuit. Then the tap switch B is next closed connecting the preventive reactor 1 in shunt between tap points 4 and I3, thus applying a voltage to the conductor 6 that corresponds to the voltage on the transformer winding I at a point mid-way between the two tap points 4 and I3. This sequence of operation is continued as shown by the chart in Fig. 4 so that, for every alternate tap position 3, 5, 1 and S, both ends of the reactor 1 will be connected through the short-circuiting switch F to one of the tap points I3, I4, I and IB while at the intermediate positions in the operation of the tap equipment 4, 6, and 8, the reactor winding 1 will be connected between adjacent tap points in the series along the winding I in a manner similar to that corresponding to position 2 of the tap-changing equipment.

In order to increase the value of current that can be conducted from a tapped point to the j conductor 6, two tap switches may be connected in parallel as shown in Fig. 2, such as A, A;

B, B'; C, C; etc. The system shown in Fig. 2 is similar to that shown in Fig. 1 except for the use of two switches A, A' in place of the single switch A, etc., for the various switches associated with the several tap points of the winding. When a circuitarrangement, such as that shown in Fig. 2, is employed, the current is very likely not to divide evenly between the two switches in parallel because of the difference in the contact resistances of the switch so that the rating of the two switches as a unit can not be double that of a single switch of the same size.

In order to force an equal division of current between the two parallel switches, there is provided an arrangement of the tap-changing circuit connections, as shown in Fig. 3.

A portion of a transformer winding 4I is shown, the terminal 44 being supplied by a current conductor 42 and the opposite terminal and conductor being connected similarly to Fig. 1 but not shown, for the purpose of enlarging the diagram covering that portion of the winding including the tap points thereof. A secondary circuit conductor 46 is shown connected to the mid-points 49 and 50 of two preventive reactors 41 and 48, respectively, which are used in place of the single preventive reactor 41 in Figs. 1 and 2. The terminal or tap point 44 is shown connected to the upper contact member of the pair of tap switches A and A and successive tap points 53, 54, 55 and 56 are shown equally spaced along the winding 4I and connected respectively to the upper contacts of cooperating pairs of tap switches B and B', C and C', D and D', E and E. The preventive reactor 41 is provided with a pair of terminals 6I and 62 connected to opposite ends thereof and the preventive reactor 48 is provided with terminals 63 and 64 at the opposite ends thereof. A pair of rst and second conductors 65 and 66 are provided connected to the like ends 62 and 64, respectively, of the pair of reactor windings 41 and 48. Another pair of first and second conductors 61 and 58 are connected to the opposite like ends 6I and 63, respectively, of the pair of reactor windings 41 and 48. The conductor 65 connects to switch B' and D and the conductor 66 to switches B and D so that whenever either pair of tap switches B and B or D and D close, the tap points 53 and 55 will be connected to the like terminals 62 and 64 of the reactors 41 and 48. Likewise, the conductor 61 is connected to switch terminals A', C' and E and the conductor 68 is connected to switch terminal A, C and E, so that whenever the pair of tap switches A and A', C and C', or E and'E' are closed, the tap points 44, 54 or 56 on the transformer winding will be connected to both terminals 6I and 63 comprising like ends of the pair of reactor windings 41 and 48. A pair of short-circuiting switches F and F are provided which operate together to a circuiteclosing or circuit-opening position and which connect the opposite ends of the pair of preventive reactors 41 and 48 together. For example, the switch F connects the terminal 62 of the preventive winding 41 to the opposite terminal 63 of the winding 48 and the switch F connects the terminal 64 of the reactor winding 40 to the opposite terminal 6I of the reactor winding 41. The chart in Fig. 4 applies equally to the circuit arrangement shown in Fig. 3, it being understood that with the operation of each one of the switches shown in the chart of Fig. 4, the correspondingly lettered and primed switch is in a similar position. Each pair of switches A and A', B and-B', etc., open together and close together.

With the circuit arrangement shown in Fig. 3, when the equipment is in position I to which the switches A and A', F and F' are in their circuit closing positions, all four end terminals 6I, 62, 63 and 64 of the two reactor windings 41 and 48 ar connected through the switches A and A to the tap point 44 so that current will flow from the tap point 44 to the end terminals of both preventive reactors 41 and 48 and to the midposition of each and from these mid-positions 49 and 50 to the circuit conductor 46. In the second tap position, indicated by the numeral 2 in Fig. 4, the switches A and A', B and B are closed and all other switches of the system are in their open position. Current will flow from the tap point 44 through switch A to the end terminal 63 of preventive reactor Winding 48 and also from tap point 44 through switch A' to the like end terminal 5I of the preventive reactor winding 41, and from these two end points to the conductor 46 through mid-points 49 and 50 of the two reactor windings. Likewise, current Will flow from the tap position 53 through switch B to the end terminal 64 of the reactor winding 48 and from tap point 53 through switch B' to the like end terminal 62 of the preventive reactor winding 41 and from these two end terminals 64 and 62 toward the midpoints 48 and 50 of their respective reactor windings to the circuit conductor 4B. Because the current to the circuit conductor 46 is required to flow through switches A and B to the :of :switches 'being :cmected with the opposite ends ofthe lpreventive reactor winding 40 and the midpoint ASII `'thereof and 'likowise through switches A" and B' to the opposite terminals 61 and`62 of afpreventivereactor'wind- `ing 'I1 that is Isimilar in character to the yprevcntive winding 48 and from the 'mid-point 49 thereof, there vare `four equal reactor lwinding portions between "each vone of the four switches A, A', B, B and the conductor IG arranged to permit a ready flow of current toward the 'midtap lpoints y49 and 50 but to prevent the how of current ybetween the 'end' terminals of the lreactor windings. It follows vthat the current iiowing 'through the several "tap yswitches A, A', B, B kremain substantially equal. "This `is equally true 'in each kof the positions 4, Vv6 and '8 `of the tapchanging equipment in which the reactor windings B1 and `48 are connected fbetween adjacentk tap positions 53 and l54, 54 an'd 55, or 55 and 56, as'will be `seen by reference to the chart in Fig. 4.

Modifications in .the apparatus and circuits illustrated .and described will occur to those skilled in the art and I do not wish .to be `otherwise limited than l"by the scope of the appended claims.

Iclaim as my invention:

1. In .a tap-changing system for transformers, a primary power circuit comprising apair of Aconductors, a .transformer energized from :said power circuit and provided with a plurality of tap conn -nectiona a Ipair of tap'bridg-ing reactor windings` .a .secondary .circuit conductor connected to vthe midpoint of each of said reactor windings, -apair of tap switches associated with each tap connection, `the pairs of .tapswitches connected with alternate .tap connections in the series being .connected and .arranged to .simultaneously connect rva. corresponding .end of each Tof said reactor windings to a tap connection, andthe ,remaining pairs of switches being .connected with theremaining alternate :tap connections in the series and arranged tosimultaneously `connect the opposite ends of each :of said reactor Awindings to .atap connection, and means ifor operating said several pairs of tap switches Ain .sequence to connect one end of the two reactor` windings-to one tap connection, `then the ,other end ofthe two :reactor windings to the 'next vadjacent ytap con- ,nection'inthe'series to connect the pair of reactor windings 'in parallel with sa ,portion of ythe-transformer winding between Atwo adjacent tap connections, then `to disconnect the 'first-named ends of the two reactor windings from the 'first-'named tap connection, .and in continuing the @sequence `of :tap switch operations to alternately connect one :end oi' the pair of reactor windings vto -successive vtap connections and then between adjacent ones of 'the plurality .of ltap connections so as to `maintainatall times an equal division of rcurrent between the parallel connected tap switches Vassociated 'with any tap connection.

2. 'In a tap-changing system for'transformers, a primary `power circuit comprising a pair of conductors, a transformer energized from said power circuit and provided with a xplurality of tap connections, a -pair of tap bridging reactor windings, a secondary lcircuit conductor connected to the midpoint of each of said reactor windingsa pair of tap switches associated with each tap connection, the pairs of tap switches connected with alternate tap connections in the series being connected and arranged to simultaneously connect a corresponding end of each of said reactor windings to a tap connection, and the remaining pairs alternate ytap connections .in .the l'series and arranged to simultaneously connect the opposite ends -of each'of said reactor windings to a tap connectionand'means for operating saidseveral pairsof tap switches in ,sequence to connect one vendor the'two Areactor windings to .one :tap conthen the 4other end .of lthe vtwo reactor windings to the rnext adjacent .tap connection 1n lthe .series-to connect the -pair of 4reactor windings iin parallel with a portion of the transformer `winding between. two adjacent tap connections, en to .disconnect the 'first-named .ends of the two reactor windings from the first-named tap connection, Aand in Vcontinuing the sequence .of tap switch operations to `alternately connect one end of the :pair of reactor windings to `successive tap.connections and then between adjacent ones 4of 'thefplurality of tap connections, and an additional pairof switches, each adapted to connect one end of one .of the pair of reactor windings Vto the opposite end :of the other one .of Athe pair of reactor windings, and .arranged'to be operated Yto a Vcircuit-closing position when the pair of :reactor :wind-ings are connected to one tap connection f-only..

S3. In a :tap-changing system for transformers, a primary :power circuit comprising a pair of .conductors a transformer energized from "said maining pairs of switches being connected with the remaining alternate tap connections in vthe series and Varranged to simultaneously vconnect 'ftheoppositeends `ofeach of .said reactorwindings to atap connection, and means for operating said several pairs of tap yswitches in sequence to connect one'end of the ltwo reactor windings to yone tap connection, vthen the other end of lthe two reactor windings to the next adjacent tap connection'in the `series to -connect the pair of -reactor windings in parallel with a portion ofthe ltransformer winding between two adjacent tap -connections, then -to disconnect the iirst-named ends of the two reactor'windings from the rstnamedtap connection, and in continuing the sequence of tap switch operations to alternately Yconnect one end of the pair of reactor vwindings to successive vtap connections and then between adjacent 4ones ofthe plurality of tap connections so as to maintain .at all times ,an equal division of ycurrent between the parallel connected tap switches associated with any tap connection, land ajpair of short-circuiting switches simultaneously operated for connecting the opposite ends of the two reactor windings to a tap connection when one Vpair only of the tap switches are ,in

f their circuit closing positions.

4. In a tap-changing system for transformers, a primary power circuit comprising a ,pair of conductors, .a transformer .energized 'from .said power circuit and provided with a plurality of tap connections, a pair of tap bridging reactor windings, a secondary circuit conductor connected to the midpoint of each of said reactor windings, a pair of tap switches associated with each tap connection, the pairs of tap switches connected with alternate tap connections in the series being connected and arranged to simultaneously connect a corresponding end of each of said reactor windings to a tap connection, and the remaining pairs of switches being connected with the remaining alternate tap connections in the series and arranged to simultaneously connect the opposite ends of each of said reactor windings to a tap connection, and a pair of short-circuiting switches simultaneously operated for connecting the opposite ends of the two reactor windings together through a pair of tap switches and the associated tap connection, the several pairs of tap switches heing arranged to operate in sequence to close the tap switches associated with the first tap connection together with the pair of short circuiting switches, to then close the tap switches associated with the next tap connection in the series of tap connections, to then open the tap switches associated with the first tap connection, then to close the pair of short-circuiting switches, and to continue this sequence of peration to connect corresponding ends of the two reactor windings to one tap connection, then the other end of the two reactor windings to the next adjacent tap connection in the series, so as to connect the pair of reactor windings in parallel with a position of the transformer winding between two adjacent tap connections, then to disconnect the rst-named ends of the two reactor windings from the first-named tap connection, and to continue the sequence of tap switch operations to alternately connect one end of the pair of reactor windings, to a tap connection, and then to connect opposite ends of the pair of reactor windings to adjacent tap connections continuing the operation to include, in sequence, the several of the plurality of tap connections.

5. In a transformer tap-changing-under-load system of the type in which the opposite terminals of a mid-tapped reactor are connected in alternate steps to successive tap points along a transformer winding, the combination with a pair of reactors having their midpoints connected to the same circuit conductor, a pair of switches associated with each tap point of the transformer winding for simultaneously connecting correspending terminals of the pair of reactors to the same tap point and simultaneously disconnecting the corresponding ends ofthe pair of reactors from the same tap point, and a pair of simultaneously operated short-circuiting switches for short circuiting the one or the other of the two reactors through one of two adjacent tap points of the transformer winding, said pair of shortcircuiting switches being simultaneously operative to circuit closing positions when a pair of switches connected to one end only of the reactor windings are in circuit closing position.

6. In combination, a transformer winding provided with a plurality of tap points, a circuit conductor, means for connecting said circuit conductor to selected tap points of the transformer winding including a pair of mid-tapped reactor windings having their mid-points connected to said circuit conductor and pairs of ratio adjusting tap-changer switches simultaneously connecting corresponding ends of both reactor windings to a selected tap point and arranged to connect alternate tap points of the transformer winding to opposite ends of the reactor windings, and a pair of simultaneously operated short-circuiting switches for short circuiting said reactor windings, said short-circuiting switches being operated to a closed circuit position only when one end of said reactor windings are connected to a tap point of the transformer winding to short circuit one of said reactor windings through the pair of ratioadjusting tap-changing switches associated with that tap point.

7. In combination, a transformer winding provided with a plurality of tap points, a circuit conductor, means for connecting said circuit conductor to selected tap points of the transformer winding including a pair of mid-tapped reactor windings having their mid-points connected to said circuit conductor and pairs of ratio-adjusting tap-changer switches simultaneously connecting corresponding ends of both reactor windings to a selected tap point and arranged to connect alternate tap points of the transformer winding to opposite ends of the reactor windings, and a pair of simultaneously operated short circuiting switches for short circuiting said reactor windings, said pair of short-circuiting switches being arranged to connect like ends of each of the pair of reactor windings to the opposite end of the other one of the pair of reactor windings, the short-circuiting switches being arranged to operate to closed circuit positions when one end only of said reactor windings are connected to a tap point on the transformer winding to short circuit one of said reactor windings through the pair of ratio adjusting tap-changing switches associated with that tap point.

8. In combination, a transformer winding` provided with a plurality of tap points, a main circuit conductor, means for connecting said circuit conductor to selected tap points including a pair of reactors each having a winding having a mid-tap connected to said main circuit conductor and each having a pair of end terminals, a pair of first and second conductors connected to like ends of the pair of reactor windings, another pair of first and second conductors connected to the opposite like ends of the pair of reactor windings1 a pair of ratio-adjusting tap changer switches associated with each tap point on the transformer winding for simultaneously connecting the tap point to one of the pairs of first and second conductors, the pair of ratio-adjusting tap-changer switches associated with any tap point being adapted to connect with the other one of the two pairs of first and second conductors then the pair of ratio-adjusting tap-changer switches associated with adjacent tap points on the transformer winding, and a pair of simultaneously operated shortcircuiting switches for short circuiting said reactor windings, said pair of short-circuiting switches being arranged to connect like ends of each of the pair of reactor windings to the opposite end of the other one of the pair of reactor windings, the short-circuiting switches being arranged to operate to a closed circuit position when one end only of said reactor windings are connected to a tap point on the transformer winding to short circuit one of said reactor windings through the pair of ratio-adjusting tap changing switches associated with that tap point.

ALEXANDER POTTINGER. 

